This invention relates to measuring the amount of particulate toner in a hopper, such as the measuring of remaining toner in an electrostatic imaging device. More specifically, this invention relates to measuring toner by determining the torque required to drive a toner paddle where the torque (or a derivative measurement) is proportional to the amount of toner through which the paddle moves.
A toner cartridge from which the current level of toner is measured at the printer using the data processing apparatus of the printer is disclosed in U.S. Pat. No. 5,634,169, assigned to the assignee to which this application is assigned. This discloses a torsion spring mounted drive to the toner-stirring paddle, which rotates in the hopper containing toner. When the toner reaches a certain level of depletion, the torsion spring yields less and less as the toner is depleted. The shaft to the toner paddle carries an encoder wheel, which may have multiple slots or other indicia for observation, but for the purpose of measuring toner, need only have spaced beginning and end slots. The time between observing the beginning slot and the end slot is related in a known amount to toner quantity, and pertinent factors are stored and the necessary data processing is carried out at the printer. Because of the varying postures of toner which occur in a hopper with stirring paddle, a running average is employed as the current toner-quantity measurement, a typical average being that of the last five paddle revolutions.
In practice known printers employing the foregoing torsion-measuring system employed an electric drive motor which produced information pulses at predetermined locations of the drive motor. This accurately defined the amount of movement to the torsion spring regardless of acceleration or deceleration. This invention avoids the expense of the hardware to provide those information pulses, and provides accurate results which provide for acceleration, deceleration, and steady state even though the operation of the printer may be interrupted prior to reaching steady state, and then resumed for a later printing operation.
In accordance with this invention the movement of a paddle driven through toner from a yieldable drive, which may be a torsion spring in an embodiment, is determined by scaling time period values during acceleration and deceleration and by treating steady state periods of movement as having a fixed value, which conceptually is a value of one for a given time period. During the same time period, the amount of movement in acceleration or deceleration will be less than the amount of movement at steady state.
As in the prior system, a tracking device with indicia, which may be an encoder wheel in an embodiment, has a recognizable home window (recognized as being wide in the embodiment) and a recognizable toner-sensing window spaced from the home window (recognized as being narrow in the embodiment). The amount of delay relative to movement of the drive to the torsion spring and of the movement between the home window and the toner sensing window represents yield at the torsion spring and is a measurement of the amount of remaining toner in the hopper in which the paddle turns.
To determine the actual movement of the drive to the torsion spring a conversion formula is stored (preferably by a look-up table) defining empirical data relating the amount of drive movement to the torsion spring to time periods. Similarly, a conversion formula is stored defining amount of movement during acceleration or deceleration depending on time of acceleration or deceleration. For steady state operation a single factor is stored.
Since the machine control software initiates all acceleration and decelerations, each initiation is used to start timings and calculations. Both the movements during acceleration and during deceleration are timed, scaled by the conversion formula, and summed, thus defining the location of the windows and the amount of yield. When steady state is reached, of course, then the amount of one unit for each time period is added. An acceleration and deceleration sequence performed without reaching steady state is scaled using the factors for the acceleration and deceleration with no unit factor.
Drive motors typically provide a xe2x80x9clockxe2x80x99 signal showing they are about to enter steady state status. Although that signal might be used to define the beginning of steady state operation, the conversion formula inherently provides the same information and can be used to define the beginning of steady state operation. In either case this invention eliminates the need for any apparatus at the printer to provide positional feedback signals.